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class="site-page"><i class="fas fa-bars fa-fw"></i></a></div></div></nav><div id="post-info"><h1 class="post-title">2-DQL数据查询语言</h1><div id="post-meta"><div class="meta-firstline"><span class="post-meta-date"><i class="far fa-calendar-alt fa-fw post-meta-icon"></i><span class="post-meta-label">Created</span><time class="post-meta-date-created" datetime="2021-03-27T15:10:45.000Z" title="Created 2021-03-27 23:10:45">2021-03-27</time><span class="post-meta-separator">|</span><i class="fas fa-history fa-fw post-meta-icon"></i><span class="post-meta-label">Updated</span><time class="post-meta-date-updated" datetime="2021-03-27T15:21:22.000Z" title="Updated 2021-03-27 23:21:22">2021-03-27</time></span></div><div class="meta-secondline"><span class="post-meta-separator">|</span><span class="post-meta-pv-cv" id="" data-flag-title="2-DQL数据查询语言"><i class="far fa-eye fa-fw post-meta-icon"></i><span class="post-meta-label">Post View:</span><span id="busuanzi_value_page_pv"></span></span></div></div></div></header><main class="layout" id="content-inner"><div id="post"><article class="post-content" id="article-container"><h1 id="DQL查询语言"><a href="#DQL查询语言" class="headerlink" title="DQL查询语言"></a>DQL查询语言</h1><h2 id="DQL基础查询语句–SELECT"><a href="#DQL基础查询语句–SELECT" class="headerlink" title="DQL基础查询语句–SELECT"></a>DQL基础查询语句–SELECT</h2><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br></pre></td><td class="code"><pre><span class="line"># DQL基础查询语句</span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">语法：</span></span><br><span class="line"><span class="comment">SELECT 查询列表 FROM 表名;</span></span><br><span class="line"><span class="comment">FROM可省</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">特点：</span></span><br><span class="line"><span class="comment">1. 查询列表可以是：表中的字段，常量，表达式，函数</span></span><br><span class="line"><span class="comment">2. 查询的结果是一个虚拟表格</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"># 选中指定库</span><br><span class="line">USE myemployees;</span><br><span class="line"></span><br><span class="line"># 查询表中的单个字段</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> last_name <span class="keyword">FROM</span> employees;</span><br><span class="line"></span><br><span class="line"># 查询表中的多个字段，中间用逗号隔开，对顺序无要求</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> last_name,first_name,email <span class="keyword">FROM</span> employees;</span><br><span class="line"></span><br><span class="line"># 查询所有字段</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> employees;</span><br><span class="line"></span><br><span class="line"># `列名`,注意可以用反单引号标注列名（不是单引号！），主要是避免列名和关键字相同的情况</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	`salary`</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees;</span><br><span class="line"></span><br><span class="line"># 查询常量值</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> <span class="number">100</span>;</span><br><span class="line"><span class="keyword">SELECT</span> <span class="string">&#x27;Steven&#x27;</span>;</span><br><span class="line"></span><br><span class="line"># 查询表达式</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> <span class="number">98</span><span class="operator">*</span><span class="number">10</span>;</span><br><span class="line"></span><br><span class="line"># 查询函数</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> VERSION();</span><br><span class="line"></span><br><span class="line"># 起别名，类似定义变量名</span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment"> * 1. 便于理解</span></span><br><span class="line"><span class="comment"> * 2. 如果查询字段有重复情况，使用别名可以便于区分</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> </span><br><span class="line"> # 方式<span class="number">1</span> 使用<span class="keyword">AS</span>关键字</span><br><span class="line"><span class="keyword">SELECT</span> <span class="number">100</span><span class="operator">*</span><span class="number">5</span> <span class="keyword">AS</span> <span class="keyword">result</span>;</span><br><span class="line"><span class="keyword">SELECT</span> last_name <span class="keyword">AS</span> 姓,first_name <span class="keyword">AS</span> 名 <span class="keyword">FROM</span> employees;</span><br><span class="line"></span><br><span class="line"># 方式<span class="number">2</span> 使用空格，别名中有特殊空格就加上双引号避免歧义</span><br><span class="line"><span class="keyword">SELECT</span> last_name 姓,first_name 名 <span class="keyword">FROM</span> employees;</span><br><span class="line"></span><br><span class="line"># 去重 利用<span class="keyword">DISTINCT</span>关键字</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> <span class="keyword">DISTINCT</span> department_id <span class="keyword">FROM</span> employees;</span><br><span class="line"></span><br><span class="line"># <span class="operator">+</span>号的作用</span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment"> * 在sql语言中+号只有一个功能就是作为运算符，不具备连接两个字段的能力</span></span><br><span class="line"><span class="comment"> * 两个操作数都为数值型可以用来作运算</span></span><br><span class="line"><span class="comment"> * 其中一方为字符型，首先会试图将字符型转换为数值型，转换成功继续运算，转换失败，则将字符型转换为0</span></span><br><span class="line"><span class="comment"> * 如果一方为null，则结果必为null</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> </span><br><span class="line"> </span><br><span class="line"># 加入想要拼接两个字段，需要采用concat()方法</span><br><span class="line"><span class="keyword">SELECT</span> CONCAT(last_name,<span class="string">&#x27; &#x27;</span>,first_name) <span class="keyword">AS</span> 姓名 <span class="keyword">FROM</span> employees;</span><br></pre></td></tr></table></figure>


<h3 id="DQL条件查询语句"><a href="#DQL条件查询语句" class="headerlink" title="DQL条件查询语句"></a>DQL条件查询语句</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br></pre></td><td class="code"><pre><span class="line"># DQL条件查询语句</span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">语法：</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">	SELECT</span></span><br><span class="line"><span class="comment">			查询列表</span></span><br><span class="line"><span class="comment">	FROM</span></span><br><span class="line"><span class="comment">			表名</span></span><br><span class="line"><span class="comment">	WHERE</span></span><br><span class="line"><span class="comment">			筛选条件</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">注意：</span></span><br><span class="line"><span class="comment">这里语句的执行顺序与我们直观上的书写顺序并不一致</span></span><br><span class="line"><span class="comment">在上面的语句中首先执行FROM语句获取读取的表</span></span><br><span class="line"><span class="comment">然后执行WHERE语句，确定筛选的条件，最后才执行SELECT语句进行查询</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">分类：</span></span><br><span class="line"><span class="comment">1. 利用条件表达式筛选：基本的条件运算符有&gt;,&lt;,=,!=,&lt;&gt;,&gt;=,&lt;=  (!=和&lt;&gt;是等价的，但推荐采用&lt;&gt;表示不等)</span></span><br><span class="line"><span class="comment">2. 按逻辑表达式查询：逻辑运算符有： &amp;&amp;,||,!,AND,OR,NOT  (推荐采用后三种)</span></span><br><span class="line"><span class="comment">3. 模糊查询：关键词有：LIKE,BETWEEN AND,IN,IS NULL</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 按条件表达式进行筛选</span><br><span class="line"></span><br><span class="line"># 筛选工资大于<span class="number">12000</span>的人</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	<span class="operator">*</span> </span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	salary<span class="operator">&gt;</span><span class="number">12000</span>;</span><br><span class="line">	</span><br><span class="line"># 查询部门编号不等于<span class="number">90</span>号的员工姓名和部门编号</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	CONCAT(first_name,<span class="string">&#x27; &#x27;</span>,last_name) 姓名,department_id 部门编号</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	department_id<span class="operator">&lt;&gt;</span><span class="number">90</span>;</span><br><span class="line">	</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 按逻辑表达式筛选</span><br><span class="line"></span><br><span class="line"># 查询工资再<span class="number">10000</span><span class="number">-20000</span>之间的员工部分信息</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	first_name,</span><br><span class="line">	last_name,</span><br><span class="line">	salary,</span><br><span class="line">	commission_pct </span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees </span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	salary <span class="operator">&gt;</span> <span class="number">10000</span> <span class="keyword">AND</span> salary <span class="operator">&lt;</span> <span class="number">20000</span>;</span><br><span class="line">	</span><br><span class="line"># 查询工资高于<span class="number">15000</span>，或者部门编号不为<span class="number">90</span>的员工</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	salary,</span><br><span class="line">	department_id</span><br><span class="line"><span class="keyword">FROM</span> </span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	salary<span class="operator">&gt;</span><span class="number">15000</span> <span class="keyword">OR</span> department_id<span class="operator">&lt;&gt;</span><span class="number">90</span>;</span><br><span class="line">	</span><br><span class="line">	</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 模糊查询</span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment"> like:和通配符搭配使用</span></span><br><span class="line"><span class="comment"> 通配符包括：</span></span><br><span class="line"><span class="comment"> %：任意多个字符，包含0个字符</span></span><br><span class="line"><span class="comment"> _：任意单个字符</span></span><br><span class="line"><span class="comment"> */</span></span><br><span class="line"> </span><br><span class="line"> </span><br><span class="line"> <span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	salary</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	last_name <span class="keyword">LIKE</span> <span class="string">&#x27;_o__h%&#x27;</span>;</span><br><span class="line">	</span><br><span class="line">#假设要查询的内容中包含通配符，可以用转义字符解释内容,或用转义关键字</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	job_id,</span><br><span class="line">	salary</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	job_id <span class="keyword">LIKE</span> <span class="string">&#x27;__\_%&#x27;</span>;</span><br><span class="line">	</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	job_id,</span><br><span class="line">	salary</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	job_id <span class="keyword">LIKE</span> <span class="string">&#x27;__$_%&#x27;</span> <span class="keyword">ESCAPE</span> <span class="string">&#x27;$&#x27;</span>;</span><br><span class="line">	</span><br><span class="line">	</span><br><span class="line">	</span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">BETWEEN AND</span></span><br><span class="line"><span class="comment">在。。。之间</span></span><br><span class="line"><span class="comment">使用BETWEEN AND可以提高语句简介程度</span></span><br><span class="line"><span class="comment">搜索结果包含两个端点值</span></span><br><span class="line"><span class="comment">两个临界值顺序不可以颠倒</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">BETWEEN AND实际等价于a&lt;=X&lt;=b,所以顺序不可颠倒</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line">#查询员工号在<span class="number">100</span><span class="number">-120</span>之间</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	<span class="operator">*</span></span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	employee_id <span class="keyword">BETWEEN</span> <span class="number">100</span> <span class="keyword">AND</span> <span class="number">120</span>;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">IN 关键字</span></span><br><span class="line"><span class="comment">判断某字段的值是否属于in列表中的某一项</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">使用in提高语句整洁度</span></span><br><span class="line"><span class="comment">in列表中的值必须是同一类型或相互兼容</span></span><br><span class="line"><span class="comment">in列表中不支持通配符</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">IN实际等价于X=a OR X=b or X=c,但是通配符在like关键字下使用</span></span><br><span class="line"><span class="comment">所以IN列表中不允许出现通配符</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	job_id</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	job_id <span class="keyword">IN</span>(<span class="string">&#x27;IT_PROG&#x27;</span>,<span class="string">&#x27;AD_VP&#x27;</span>,<span class="string">&#x27;AD_PRES&#x27;</span>);</span><br><span class="line">	</span><br><span class="line">	</span><br><span class="line">	</span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">IS NULL关键字  (IS NOT NULL)</span></span><br><span class="line"><span class="comment">判断是否为NULL值</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">(在SQL语言中＝号或者&lt;&gt;不能判断是否为NULL值)</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	commission_pct</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	commission_pct <span class="keyword">IS</span> <span class="keyword">NULL</span>;</span><br><span class="line">	</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">安全等与 &lt;=&gt;</span></span><br><span class="line"><span class="comment">安全等于可以用来判断NULL值，也可以用来判断普通类型的值</span></span><br><span class="line"><span class="comment">缺点是可读性较低</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	commission_pct,</span><br><span class="line">	job_id</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	job_id <span class="operator">&lt;=&gt;</span> <span class="string">&#x27;SA_REP&#x27;</span> <span class="keyword">OR</span> commission_pct <span class="operator">&lt;=&gt;</span> <span class="keyword">NULL</span>;</span><br><span class="line">	</span><br></pre></td></tr></table></figure>


<h3 id="DQL排序查询语句"><a href="#DQL排序查询语句" class="headerlink" title="DQL排序查询语句"></a>DQL排序查询语句</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br></pre></td><td class="code"><pre><span class="line"># DQL排序查询语句</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">语法：(【】表示可省)</span></span><br><span class="line"><span class="comment">SELECT</span></span><br><span class="line"><span class="comment">	查询列表</span></span><br><span class="line"><span class="comment">FROM</span></span><br><span class="line"><span class="comment">	表名</span></span><br><span class="line"><span class="comment">【WHERE 筛选条件】</span></span><br><span class="line"><span class="comment">ORDER BY</span></span><br><span class="line"><span class="comment">	排序列表 【asc|desc】</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">特点：</span></span><br><span class="line"><span class="comment">ASC代表升序，DESC代表降序。不写的情况下默认升序</span></span><br><span class="line"><span class="comment">ORDER BY字句一般放在整个查询语句的最后（LIMIT字句除外）</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"># 工资由高到低排序</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	<span class="operator">*</span></span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	salary <span class="keyword">DESC</span>;</span><br><span class="line">	</span><br><span class="line"># 由低到高</span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> employees <span class="keyword">ORDER</span> <span class="keyword">BY</span> salary <span class="keyword">ASC</span>;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 排序<span class="operator">+</span>筛选  查询部门编号<span class="operator">&gt;=</span><span class="number">90</span>的员工信息，按入职时间的先后进行排序</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	department_id,</span><br><span class="line">	hiredate </span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees </span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	department_id <span class="operator">&gt;=</span> <span class="number">90</span> </span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	hiredate;</span><br><span class="line">	</span><br><span class="line"></span><br><span class="line"># 按表达式排序  年薪降序</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	last_name,</span><br><span class="line">	salary<span class="operator">*</span><span class="number">12</span><span class="operator">*</span>(<span class="number">1</span><span class="operator">+</span>IFNULL(commission_pct,<span class="number">0</span>)) 年薪</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	salary<span class="operator">*</span><span class="number">12</span><span class="operator">*</span>(<span class="number">1</span><span class="operator">+</span>IFNULL(commission_pct,<span class="number">0</span>)) <span class="keyword">DESC</span> ;</span><br><span class="line"></span><br><span class="line"># 用别名排序</span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	last_name,</span><br><span class="line">	salary<span class="operator">*</span><span class="number">12</span><span class="operator">*</span>(<span class="number">1</span><span class="operator">+</span>IFNULL(commission_pct,<span class="number">0</span>)) 年薪</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	年薪 <span class="keyword">DESC</span> ;</span><br><span class="line"></span><br><span class="line"># 用函数排序</span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	last_name,</span><br><span class="line">	salary,</span><br><span class="line">	LENGTH(last_name) <span class="keyword">AS</span> 长度</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	LENGTH(last_name) ;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 按多个字段排序</span><br><span class="line"># 先按工资升序，再按员工编号降序</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	salary,</span><br><span class="line">	employee_id</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	salary <span class="keyword">ASC</span>,</span><br><span class="line">	employee_id <span class="keyword">DESC</span>;</span><br></pre></td></tr></table></figure>


<h3 id="排序查询"><a href="#排序查询" class="headerlink" title="排序查询"></a>排序查询</h3><figure class="highlight sql"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br></pre></td><td class="code"><pre><span class="line"># DQL排序查询语句</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/*</span></span><br><span class="line"><span class="comment">语法：(【】表示可省)</span></span><br><span class="line"><span class="comment">SELECT</span></span><br><span class="line"><span class="comment">	查询列表</span></span><br><span class="line"><span class="comment">FROM</span></span><br><span class="line"><span class="comment">	表名</span></span><br><span class="line"><span class="comment">【WHERE 筛选条件】</span></span><br><span class="line"><span class="comment">ORDER BY</span></span><br><span class="line"><span class="comment">	排序列表 【asc|desc】</span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment"></span></span><br><span class="line"><span class="comment">特点：</span></span><br><span class="line"><span class="comment">ASC代表升序，DESC代表降序。不写的情况下默认升序</span></span><br><span class="line"><span class="comment">ORDER BY字句一般放在整个查询语句的最后（LIMIT字句除外）</span></span><br><span class="line"><span class="comment">*/</span></span><br><span class="line"></span><br><span class="line"># 工资由高到低排序</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	<span class="operator">*</span></span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	salary <span class="keyword">DESC</span>;</span><br><span class="line">	</span><br><span class="line"># 由低到高</span><br><span class="line"><span class="keyword">SELECT</span> <span class="operator">*</span> <span class="keyword">FROM</span> employees <span class="keyword">ORDER</span> <span class="keyword">BY</span> salary <span class="keyword">ASC</span>;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 排序<span class="operator">+</span>筛选  查询部门编号<span class="operator">&gt;=</span><span class="number">90</span>的员工信息，按入职时间的先后进行排序</span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	department_id,</span><br><span class="line">	hiredate </span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees </span><br><span class="line"><span class="keyword">WHERE</span></span><br><span class="line">	department_id <span class="operator">&gt;=</span> <span class="number">90</span> </span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	hiredate;</span><br><span class="line">	</span><br><span class="line"></span><br><span class="line"># 按表达式排序  年薪降序</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	last_name,</span><br><span class="line">	salary<span class="operator">*</span><span class="number">12</span><span class="operator">*</span>(<span class="number">1</span><span class="operator">+</span>IFNULL(commission_pct,<span class="number">0</span>)) 年薪</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	salary<span class="operator">*</span><span class="number">12</span><span class="operator">*</span>(<span class="number">1</span><span class="operator">+</span>IFNULL(commission_pct,<span class="number">0</span>)) <span class="keyword">DESC</span> ;</span><br><span class="line"></span><br><span class="line"># 用别名排序</span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	last_name,</span><br><span class="line">	salary<span class="operator">*</span><span class="number">12</span><span class="operator">*</span>(<span class="number">1</span><span class="operator">+</span>IFNULL(commission_pct,<span class="number">0</span>)) 年薪</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	年薪 <span class="keyword">DESC</span> ;</span><br><span class="line"></span><br><span class="line"># 用函数排序</span><br><span class="line"><span class="keyword">SELECT</span> </span><br><span class="line">	last_name,</span><br><span class="line">	salary,</span><br><span class="line">	LENGTH(last_name) <span class="keyword">AS</span> 长度</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	LENGTH(last_name) ;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"># 按多个字段排序</span><br><span class="line"># 先按工资升序，再按员工编号降序</span><br><span class="line"></span><br><span class="line"><span class="keyword">SELECT</span></span><br><span class="line">	last_name,</span><br><span class="line">	salary,</span><br><span class="line">	employee_id</span><br><span class="line"><span class="keyword">FROM</span></span><br><span class="line">	employees</span><br><span class="line"><span class="keyword">ORDER</span> <span class="keyword">BY</span></span><br><span class="line">	salary <span class="keyword">ASC</span>,</span><br><span class="line">	employee_id <span class="keyword">DESC</span>;</span><br></pre></td></tr></table></figure></article><div class="post-copyright"><div class="post-copyright__author"><span class="post-copyright-meta">Author: </span><span class="post-copyright-info"><a href="mailto:undefined">Ywrby</a></span></div><div class="post-copyright__type"><span class="post-copyright-meta">Link: </span><span class="post-copyright-info"><a 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more</div></div><div class="sticky_layout"><div class="card-widget" id="card-toc"><div class="item-headline"><i class="fas fa-stream"></i><span>Catalog</span></div><div class="toc-content"><ol class="toc"><li class="toc-item toc-level-1"><a class="toc-link" href="#DQL%E6%9F%A5%E8%AF%A2%E8%AF%AD%E8%A8%80"><span class="toc-number">1.</span> <span class="toc-text">DQL查询语言</span></a><ol class="toc-child"><li class="toc-item toc-level-2"><a class="toc-link" href="#DQL%E5%9F%BA%E7%A1%80%E6%9F%A5%E8%AF%A2%E8%AF%AD%E5%8F%A5%E2%80%93SELECT"><span class="toc-number">1.1.</span> <span class="toc-text">DQL基础查询语句–SELECT</span></a><ol class="toc-child"><li class="toc-item toc-level-3"><a class="toc-link" href="#DQL%E6%9D%A1%E4%BB%B6%E6%9F%A5%E8%AF%A2%E8%AF%AD%E5%8F%A5"><span class="toc-number">1.1.1.</span> <span class="toc-text">DQL条件查询语句</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#DQL%E6%8E%92%E5%BA%8F%E6%9F%A5%E8%AF%A2%E8%AF%AD%E5%8F%A5"><span class="toc-number">1.1.2.</span> <span class="toc-text">DQL排序查询语句</span></a></li><li class="toc-item toc-level-3"><a class="toc-link" href="#%E6%8E%92%E5%BA%8F%E6%9F%A5%E8%AF%A2"><span class="toc-number">1.1.3.</span> <span class="toc-text">排序查询</span></a></li></ol></li></ol></li></ol></div></div><div class="card-widget card-recent-post"><div class="item-headline"><i class="fas fa-history"></i><span>Recent Post</span></div><div class="aside-list"><div class="aside-list-item"><a class="thumbnail" href="/2021/12/25/22-%E5%86%85%E5%AD%98%E7%A9%BA%E9%97%B4%E6%89%A9%E5%85%85%EF%BC%88%E8%A6%86%E7%9B%96%E4%B8%8E%E4%BA%A4%E6%8D%A2%EF%BC%89/" title="22-内存空间扩充（覆盖与交换）"><img src="/img/67888138_p0.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="22-内存空间扩充（覆盖与交换）"/></a><div class="content"><a class="title" href="/2021/12/25/22-%E5%86%85%E5%AD%98%E7%A9%BA%E9%97%B4%E6%89%A9%E5%85%85%EF%BC%88%E8%A6%86%E7%9B%96%E4%B8%8E%E4%BA%A4%E6%8D%A2%EF%BC%89/" 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